1. Field of the Invention
The present invention relates to an evacuation system and a method therefor for evacuating, for example, a sputtering apparatus.
2. Description of the Prior Art
A conventional evacuation system for a high vacuum sputtering apparatus includes a cryopump connected to a sputtering chamber through a valve and auxiliary pumps for performing an evacuation to obtain a pressure under which the cryopump can be actuated. The cryopump cools a baffle to an extremely low temperature of approximately 20K (absolute temperature), by using a helium refrigerator, and absorbs and exhausts gas molecules. Since the baffle is cooled to an extremely low temperature, the cryopump is excellent in exhaust ability with respect to, particularly, water. Furthermore, since the cryopump is of a storage type, even if the operation of the sputtering apparatus is stopped due to some accident, there is little influence on the outside. Therefore, a cryopump is widely used in a sputtering apparatus. However, the storage type pump is must be periodically regenerated after exhausting the gas molecules. Furthermore, since such a cryopump also has an evacuation ability with respect to argon, it is necessary to control the amount of exhausted argon gas by a valve operation in a sputtering filming apparatus using argon gas.
A cold head for cooling a baffle to approximately 150K by using a coolant is generally used to lower the pressure in a process chamber merely by increasing the exhaust amount of water molecules; or used as a cold trap to prevent oil molecules from flowing backward in an oil diffusion pump. In such cases, the cold head is connected to the process chamber through a valve, and a main pump is directly connected to the downstream side of the cold head.
In a conventional evacuation apparatus, as described above, the pumping speed with respect to gas molecules including water is as high as possible in order to shorten the time required for continuing the exhaust to obtain a desired pressure. However, since there is a limit to the pumping speed of a vacuum pump and a storage type pump such as a cryopump needs regeneration, a time period which does not contribute to production is necessary in a semiconductor manufacturing apparatus such as a sputtering apparatus. Thus, the semiconductor manufacturing apparatus requires additional time for producing the semiconductors.
In order to solve the problems relating to the additional processing time, an apparatus has been proposed which eliminates any loss of time due to the warm-up and stopping of a cooling source by switching the temperature of a coolant of a cold trap in a short time.
An apparatus of the aforementioned type is disclosed in, for example, "A User's Guide to Vacuum Technology", John F. O'Hanlon.